Program Director/Principal Investigator (Robey, Ellen, A): Abstract: Mouse Qa-1 is a member of the conserved MHC-E family of non-classical MHC-1 molecules (MHC1b). In most cells, MHC-E presents peptides derived from the leader sequences of classical (MHC1a) molecules, and regulates the function of NK cells through the germ-line encoded receptor CD94/NKG2. MHC-E molecules can also present self and pathogen-derived peptides to CD8 T cells. The signals that lead to presentation of alternative peptides by MHC-E, and the functions of the responding CD8 T cells remain poorly understood. Recently, studies of a highly effective HIV vaccine based on a CMV vector revealed a prominent MHC-E restricted CD8 T cell response, raising new interest in understanding the presentation mechanisms and in vivo functions of MHC-E. Together with our collaborators, we have been investigating a Qa-1-restricted T cell response to cells lacking the ER aminopeptidase associated with antigen processing (ERAAP ko) (Nagarajan et al., 2012). The responding CD8 T cells recognize a 9-mer peptide derived from a self-protein (FL9 from FAM49) presented by Qa-1(b) (called QFL T cells). QFL T cells use an invariant TCR a, and have characteristics of both conventional and non-conventional CD8 T cells. Our preliminary data indicate that QFL T cells encounter high affinity Qa-1 restricted ligands at steady state and during viral infection. We propose to use a newly generated TCR transgenic mouse strain to probe the in vivo generation of Qa-1 restricted ligands for QFL T cells in both steady state and during viral infection. In Aim 1, we will identify the pMHC ligands involved in positive and agonist selection of QFL T cells, and will identify the thymic cell types that present the ligands. In Aim 2, we will identify the ligand(s) that drive the homeostatic expansion of QFL T cells, and will determine when, in what tissue, and by what cell type(s) they are presented. In Aim 3, we will determine the mechanisms that lead to priming of QFL T cells during MCMV infection, and will test whether QFL T cells induced during MCMV infection can kill infected cells and provide immune protection. Our results will shed new light on how MHC-E presentation regulates T cell responses, with important implications for vaccine design. OMB No. 0925-0001/0002 (Rev. 01/18 Approved Through 03/31/2020) Page Continuation Format Page